A dishwasher is a home appliance that washes dishes by discharging high-pressure wash liquid through discharge members onto the dishes to remove impurities thereon.
In more detail, a dishwasher includes a tub forming a space inside the dishwasher for holding dishes to be washed, dish racks installed to slide in and out of the tub for holding dishes, discharge members installed inside the tub for spraying wash liquid, a sump disposed at the bottom of the tub for holding wash liquid, a wash pump assembly attached to a side of the sump for pumping the wash liquid contained in the sump to the discharge members, and a drain pump assembly for draining dirty wash liquid after dish washing is completed.
The discharge members consist of a lower arm installed above the sump, and an upper arm and a top nozzle connected to a water guide installed on an interior surface of the tub. Wash liquid is alternately pumped to the lower arm and the water guide by means of a switching valve located in the sump. In other words, during a wash cycle, the wash liquid that is alternately pumped by means of the switching valve is intermittently pumped at a predetermined interval to the lower and upper arms.
In conventional dishwashers, the running time of a dishwashing cycle and the switching intervals of the switching valve are dependant on the settings inputted by a user. Accordingly the final discharge member to discharge wash liquid before a wash cycle ends could be the upper arm or the lower arm.
However, if the lower arm is the final discharge member to discharge wash liquid in a wash cycle, the impurities present on dishes in the lower rack are sprayed up to dishes on the upper rack, resulting in impurities left on dishes after a wash cycle. However, when wash liquid is discharged from the upper arm, the dishes on the upper rack are washed, and the water settles to the bottom of the tub through gravity. Accordingly, even when the water falls on the dishes in the bottom rack, the deposits on those dishes settle and collect on the floor of the tub along with the water.
The lower arm has its spray holes defined by its upper surface (and some on its lower surface), and the lower rack is positioned directly above the lower arm. Therefore, when wash liquid is sprayed upward through the lower arm, the impurities on the dishes in the lower rack are sprayed upward onto the dishes in the upper rack and the upper walls of the tub. Resultantly, even after the wash cycle is completed, impurities are left remaining on the dishes in the upper rack, compromising dishwashing effectiveness and giving users an unsanitary impression.